Back in the '60s, the Cellar Door nightclub in Georgetown hosted Sunday night hootenannies that attracted a diverse group of singers: the club's one-man house band, Donal Leace; the transplanted Texan Allen Damron; the College Park frat brothers of the Hard Travelers, the young married couple Taffy Nivert and Bill Danoff and a Virginia high school student named Emmylou Harris. All the above singers gathered at Merriweather Post Pavilion last night for a reunion they called the third annual Hard Travelers and Friends Concert for Cystic Fibrosis.

Singer Kenn Roberts of the Hard Travelers announced that the show had raised $85,000 for the Cystic Fibrosis Foundation to fight the genetic childhood disease. The above singers were joined by the Maine sing-along trio, Schooner Fare, and the duo of Charlie Byrd & Pete Kennedy. Harris headlined the concert in an abridged version of her show at Wolf Trap earlier this summer. She was in splendid voice, obviously buoyed by the memories that sparked stories about living in Howard County and hanging out in the Danoffs' basement.

Harris led her best band in years, the Nash Ramblers, which featured mandolinist/fiddler Sam Bush of the New Grass Revival and dobroist Al Perkins of the Flying Burrito Brothers. Whether she sang a stately bluegrass hymn such as "Green Pastures" or a rockabilly raver like "Mystery Train," she led pretty three-part harmonies that were laced up by one hot solo after another.

The two best opening acts were the result of seemingly unlikely pairings. Charlie Byrd -- the balding jazz veteran with a nylon-string guitar -- and Pete Kennedy -- the curly-headed folk-rocker with the steel-string guitar -- sat next to each other and picked out old standards such as Fats Waller's "I'm Going to Sit Right Down and Write Myself a Letter." Through spirited give-and-take, they pushed each other into adventurous solos that neither would take on his own.

Even more unexpected was the reunion of Nivert and Danoff, who once tasted fame as the duo Fat City and later as one half of the Starland Vocal Band. Nivert's irreverent bluntness about their divorce was a refreshing change from the evening's earnestness, but the ex-spouses still had a musical rapport, at least as they blended harmonies on their old songs such as "Take Me Home, Country Roads."